In providing telephone service to a building, a telephone line from the telephone company is typically connected to a telephone system interface box by an overhead riser or buried underground cable. Conventional telephone wiring then runs from the telephone interface to provide the telephone service. Because the telephone system needs to be grounded, a wire of relatively low gauge is connected at one end to the telephone interface box and at its other end to an elongated ground rod sunk into the ground.
The telephone interface box itself typically mounted to a wall of the building being serviced. The telephone interface box may be mounted to the wall in any one of a variety of known ways. The telephone interface box, for example, can be bolted to the wall or attached to a bracket which is mounted to a wall. The mounting typically requires drilling holes into the wall for the bolts, screws or brackets.
While the foregoing procedure provides adequate mounting of the telephone interface box, a better method is to employ a clamp which is securable to an electric utility box. Typically, the electric utility box will already have been mounted to the wall of the building. The telephone interface box can then be connected to a plate that forms part of the clamp, eliminating the need to separately mount the telephone interface box to the wall of the building.
Such a clamp is disclosed in U.S. Pat. No. 5,018,984 issued to Franks, Jr., on May 28, 1991. The clamp disclosed in that patent is not adjustable to fit electric utility boxes of variable size. Thus, a clamp that is adjustable to the width of a particular utility box would be desirable.
When installing these interface or utility boxes, utility companies, such as providers of telephone and electric service, typically provide separate electrical grounding for each type of service. For example, an electric utility box is usually grounded by a heavy gauge wire which is connected to an elongated ground rod sunk into the nearby ground. Likewise, the adjacent telephone interface box is grounded by a wire of lower gauge which is connected to a second elongated ground typically sunk within several feet of the power ground rod.
To reduce the potential difference between the telephone interface box and electric utility box, it is necessary to connect a jumper wire or the like between the telephone system ground rod and electrical power system ground rod to prevent differences in potential which could result in electric arcing between the telephone interface box and the electric utility box in the event of lightning or accidental contact with the telephone line, for example. This procedure is complicated by the fact that it is often impossible or impractical to open or penetrate the electric utility box. Therefore, a jumper wire or the like must be installed by digging to expose the buried power ground rod.
While the foregoing procedure works, an easier and less expensive method is to employ a clamp which provides a common ground by mechanically and electrically connecting a grounding wire for the telephone interface box to the electric utility box. To be effective, such clamps must be able to penetrate dirt, corrosion and nonconductive coatings which may be on the electric utility box. They must also be able to conduct a high amperage current to ground, as might occur in a lightning strike, without premature failure. Such a clamp is disclosed in U.S. Pat. No. 5,006,074 issued to Franks, Jr. on Apr. 9, 1991. While this clamp is an excellent device for creating a single grounding system, it does not provide structure for mounting a telephone interface box on an electric utility box. Nor does the earlier-described mounting clamp provide intimate electrical contact for grounding with an electric utility box. Ideally, a single adjustable clamp would provide both grounding and mounting features.
An important feature of the existing grounding clamp disclosed in U.S. Pat. No. 5,006,074 is that it is adjustable to fit boxes of various widths. The clamp is generally U-shaped in cross section and has a base adjustable in length. Two fixed arms extend from the adjustable base. In operation, the adjustable base is adjusted to the approximate width of the electric utility box. The clamp is placed over the box, and the two fixed arms engage and bracket the box.
A limitation with the foregoing existing clamp is that its base is only adjustable in coarse graduations. A screw or bolt in one of the fixed arms provides fine adjustment. While the adjustment screw is adequate, the clamp would be stronger and more reliable if the base could be more precisely adjusted to more nearly the actual width of the box to which the clamp is applied.